EP3918663B1

EP3918663B1 - Dual port antenna structure

Info

Publication number: EP3918663B1
Application number: EP19708060.9A
Authority: EP
Inventors: Hai Zhou; Hanyang Wang
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2019-02-25
Filing date: 2019-02-25
Publication date: 2023-06-21
Anticipated expiration: 2039-02-25
Also published as: WO2020173540A1; EP3918663A1; CN113544906A; US20220149525A1; CN113544906B

Description

FIELD OF THE INVENTION

This invention relates to antenna structures, and in particular to providing a compact design for an antenna structure capable of operating in more than one mode.

BACKGROUND

An antenna is a transducer that converts radio frequency electric current to electromagnetic waves that are radiated into space in order to transmit a signal, and that also converts electromagnetic waves from space into radio frequency electric current in order to receive a signal.
Portable handheld units, such as mobile phones and tablets, are typically required to transmit and receive signals at different frequencies. For example, a mobile phone may be required to transceive cellular signals at 1.8GHz, and Bluetooth signals at 2.45GHz.
It is known to provide antenna structures in which two separate radiators are collocated: one for transceiving at a first frequency, and the other for transceiving at a second frequency. Figures 1a, 1b and 1c illustrate how a first radiator configured to resonate at a first frequency (shown individually in figure 1a) and a second radiator configured to resonate at a second frequency (shown individually in figure 1b) can be integrated to form a combined antenna structure (shown in figure 1c). The first radiator is a dipole antenna having two metal strips 101a and 101b which are fed in a differential mode with a first current from port 102, generating radiation pattern 103. The second radiator is a dipole antenna having two metal strips 104a and 104b which are fed in a common mode with a second current from port 105, generating radiation pattern 106. In the combined antenna structure shown in figure 1c, the radiation patterns generated by the individual radiators of figures 1a and 1b have little overlap and hence are well isolated from each other, thereby enabling signals of both the first and second frequencies to be transceived at the same time.
Many products into which antennas are integrated, for example mobile phones and tablets, have many internal components, all of which need to fit within a limited overall volume. It is therefore desirable to minimize the volume dedicated to each internal component, without losing performance of that component. The antenna structure of figure 1c uses two radiators, each of which generates a single resonance. It is desirable to provide an antenna structure having at least two resonances which is more compact than the structure of figure 1c whilst maintaining sufficient isolation so as to enable signals at both resonant frequencies to be transceived at the same time.
From US 2009/109104 A1 balun (balanced-unbalanced) antennas are known. From US 2017/033461 A1 low-profile antennas with high isolation for bluetooth and wifi coexistence are known. From US 2010/279734 A1 multiprotocol antenna for wireless systems are known. From US 2017/048649 A1 NFC antenna architectures for mobile communication device with single-piece metal housing are known. Further, from EP 2 963 736 A1 multi-band antenna elements and corresponding antennas are known. Further multi-band antenna structures are known from US 20017/093049 A1 and US 7 724 201 B2 .

SUMMARY OF THE INVENTION

According to a first aspect, there is provided an antenna structure comprising: a first port; a second port; and a single radiator connected to both the first and second ports, the single radiator being operable to simultaneously transceive in: a symmetrical excited mode in which current flows symmetrically through the single radiator to or from the first port, thereby causing the single radiator to resonate at a first resonant frequency; and an asymmetrical excited mode in which current flows asymmetrically through the single radiator to or from the second port, thereby causing the single radiator to resonate at a second resonant frequency. This is a compact antenna structure which is able to transceive on two frequencies at the same time whilst exhibiting high isolation.
The second resonant frequency may be the same as (or very close to) the first resonant frequency.
The single radiator may be operable to transceive in a further symmetrical excited mode in which current flows symmetrically through the single radiator to or from the first port, thereby causing the single radiator to resonate at a third resonant frequency. This enables the antenna structure to additionally transceive on a further frequency.
The single radiator may be operable to simultaneously transceive in both the symmetrical excited mode and the further symmetrical excited mode. Thus, the antenna structure is able to transceive on the first, second and third frequencies at the same time.
The single radiator may be operable to transceive in a further asymmetrical excited mode in which current flows asymmetrically through the single radiator to or from the second port, thereby causing the single radiator to resonate at a fourth resonant frequency. This enables the antenna structure to additionally transceive on a yet further frequency. The single radiator may be operable to simultaneously transceive in both the asymmetrical excited mode and the further asymmetrical excited mode. Thus, the antenna structure is able to transceive on the first, second, fourth and optionally third frequencies at the same time.
The single radiator comprises a first element, the first element being elongate and linear; a second element, the second element being elongate, linear, and parallel to the first element; and arm connectors connecting the first element to the second element. This is a compact layout.
The first element, second elements and arm connectors may form a symmetrical structure. The symmetry in the layout of the antenna structure aids in generating generally uniform radiation patterns at the resonant frequencies.
The first port may comprise a set of first port feedlines connected to the first element in a symmetrical arrangement. The symmetry in the layout of the first port aids in generating generally uniform radiation patterns in the symmetrical excited mode(s).
The antenna structure may be configured to feed a signal being transmitted or received via the first port along a central first port feedline of the set of first port feedlines. This causes a more symmetrical current flow through the radiator, and hence a more uniform radiation pattern in the symmetrical excited mode(s).
The second port comprises two second port feedlines connected to the second element in a symmetrical arrangement. The symmetry in the layout of the second port aids in generating generally uniform radiation patterns in the asymmetrical excited mode(s).
The antenna structure is configured to feed a signal being transmitted or received via the second port as a differential signal along the two second port feedlines. Feeding the second port with a differential signal generates the asymmetrical current flow in the asymmetrical mode.
The antenna structure may be configured to feed a signal being transmitted or received via the second port through a co-axial cable coupled to a balun or a microstrip coupled to a balun. Both of these feeding structures generate the asymmetrical current flow in the asymmetrical mode.
Each first port feedline and/or each second port feedline may comprise impedance matching network circuitry. This ensures efficient power transfer from the feedlines to the radiator, and prevents standing waves from establishing. The antenna structure may have a three-dimensional profile and/or be comprised partially or wholly of multiple layers. This may enable the antenna structure to fit into the shape of the available volume in, for example, the mobile phone or tablet into which the antenna structure is incorporated.
According to a second aspect, there is provided a method of operating the antenna structure comprising a first port, a second port, and a single radiator connected to both the first and second ports, the method comprising: simultaneously transceiving in: a symmetrical excited mode in which current flows symmetrically through the single radiator to or from the first port, thereby causing the single radiator to resonate at a first resonant frequency; and an asymmetrical excited mode in which current flows asymmetrically through the single radiator to or from the second port, thereby causing the single radiator to resonate at a second resonant frequency. This method enables a compact antenna structure to transceive on two frequencies at the same time whilst exhibiting high isolation.

BRIEF DESCRIPTION OF THE FIGURES

The present invention will now be described by way of example with reference to the accompanying drawings. In the drawings:

Figures 1a, 1b and 1c illustrate a known antenna structure having two collocated radiators;
Figure 2 illustrates an exemplary antenna structure according to the present invention;
Figures 3a and 3b illustrate symmetrical and asymmetrical modes of a radiator;
Figure 4 illustrates an example feeding structure for the first port of the antenna structure;
Figure 5 illustrates a current distribution for a symmetrically excited mode of the antenna structure;
Figure 6 illustrates the radiation pattern for the resonance shown in figure 5;
Figures 7 to 10 illustrate example feeding structures for the second port of the antenna structure;
Figure 11 illustrates a current distribution for an asymmetrically excited mode of the antenna structure;
Figure 12 illustrates the radiation pattern for the resonance shown in figure 11;
Figure 13 illustrates a current distribution for a symmetrically excited mode of the antenna structure;
Figure 14 illustrates the radiation pattern for the resonance shown in figure 13;
Figure 15 illustrates a current distribution for an asymmetrically excited mode of the antenna structure;
Figure 16 illustrates the radiation pattern for the resonance shown in figure 15;
Figures 17 and 18 illustrate the S parameter performance of an example embodiment of the antenna structure;
Figure 19 illustrates the Envelope Correlation Coefficient of the example embodiment of the antenna structure whose S parameter performance is shown in figures 17 and 18;
Figures 20 and 21 illustrate the S parameter performance for another example embodiment of the antenna structure; and
Figure 22 illustrates the current distributions through the antenna structure of figure 2 at the resonant frequencies of the symmetrical and asymmetrical modes.

DETAILED DESCRIPTION

Figure 2 illustrates an example antenna structure of the present invention, shown generally at 200. The antenna structure comprises a single radiator 201 connected to two ports: first port 202 and second port 203. In this example, the antenna structure 200 is connected to ground plane 204 via the first port 202. The single radiator 201 comprises a first element 205 and a second element 206, which are connected by arm connectors 207. Each of the first and second elements is elongate and linear. The first element is parallel to the second element.
In the example of figure 2, the first element 205 is shorter than the second element 206 in the direction in which they are parallel. For example, the longitudinal length L₁ of the first element 205 may be in the range 10-20mm. The longitudinal length L₂ of the second element 206 may be in the range 70-76mm. In the example of figure 2, the first element 205 is narrower than the second element 206 in the direction perpendicular to that in which they are parallel. For example, the width W₁ of the first element 205 may be less than or the same as 1mm. The width W₂ of the second element 206 may be in the range 2-3mm.
In the example of figure 2, there are two arm connectors 207, each of which connects a different end of the first element 205 to the second element 206. However, there may be more than two arm connectors 207. For example, there may be further arm connectors in between the two arm connectors illustrated on figure 2. In the example of figure 2, the arm connectors extend perpendicularly from the first element to the second element. Alternatively, the arm connectors may extend at a (non-perpendicular) angle from the first element to the second element. The arm connectors may have similar proportions to the width W₁ of the first element. For example, the arm connectors may each have a length D₁ in the direction of elongation of the first and second elements of less than or the same as 1mm. Similarly, the arm connectors may each have a length D₂ perpendicular to the direction of elongation of the first and second elements of less than or the same as 1mm.
In the example of figure 2, the second element 206 is separated from the ground plane 204 in a direction perpendicular to the direction of elongation of the second element 206 by a gap S. S may be, for example, in the range 2-3mm.
The values of L₁, L₂, W₁, W₂, D₁, D₂ and S identified above are all suitable for an implementation in which the antenna structure is incorporated into a mobile phone.
In the example of figure 2, the first element 205, the second element 206 and the arm connectors 207 form a symmetrical structure. This structure has reflectional symmetry about an axis 208 which bisects the structure in a direction perpendicular to the direction of elongation of the first and second elements. The midpoint of the longitudinal length of the first element 205 lies on the axis 208. The midpoint of the longitudinal length of the second element 206 lies on the axis 208. The symmetry of the first element, second element and arm connectors aids in generating a generally uniform radiation pattern at resonance when current is fed into the structure.
Current fed through the first port 202 causes the single radiator 201 to resonate to transceive a signal. Current fed through the second port 203 also causes the single radiator 201 to resonate to transceive a signal. Thus, the same single radiator is used to generate resonances by both the first and second ports. The first port 202 operates in a symmetrical mode, in which current flows symmetrically through the single radiator to or from the first port. Figure 3a illustrates such a symmetrical mode. Current fed through feedline 301 causes current to flow equally in both directions through the linear radiator 302. Curve 303 demonstrates the relative amplitude of the current through the radiator 302. The current amplitude peaks in the centre where the feedline meets the radiator, and falls evenly to either side from there. The second port 203 operates in an asymmetrical mode, in which current flows asymmetrically through the single radiator to or from the second port. Figure 3b illustrates such an asymmetrical mode. Current fed through feedline 304 causes current to flow in a single direction through the radiator 305. Curve 306 demonstrates the relative amplitude of the current through the radiator 305. The current amplitude peaks in the centre where the feedline meets the radiator, and falls evenly to either side from there.
The following describes exemplary arrangements of the first port 202 and second port 203 which cause current to flow through the radiator of figure 2 in symmetrical and asymmetrical modes respectively.
The first port 202 of the antenna structure 200 of figure 2 comprises a set of first port feedlines 209a, 209b, 209c. These first port feedlines feed current into the single radiator 201 from the first port. The first port feedlines connect to the first element 205. The first port feedlines connect to an opposing side of the first element 205 to the arm connectors 207. In the example of figure 2, the first port feedlines connect the ground plane 204 to the first element 205.
In figure 2, three first port feedlines are shown. However, there may be more than three first port feedlines. Alternatively, there may be fewer than three first port feedlines. In figure 2, the first port feedlines are connected to the first element 205 in a symmetrical arrangement. One first port feedline 209a connects to one end of first element 205, and another first port feedline 209c connects to the other end of first element 205. A further first port feedline 209b connects to the midpoint of first element 205. In figure 2, the combination of the first port feedlines 209a, 209b, 209c and the first element 205 form a symmetrical structure which has reflectional symmetry about the axis 208.
In figure 2, the first port feedlines extend perpendicularly to the direction of elongation of the first element 205. In figure 2, the first port feedlines are in the same plane as the remainder of the antenna structure. In other words, the first port feedlines and the single radiator 201 form a planar structure. Alternatively, the first port feedlines may extend out of the plane of the single radiator. For example, the first port feedlines may extend perpendicularly to the plane of the single radiator 201. This may aid fitting the antenna structure into the shape of the available volume of the device into which the antenna structure is integrated.
The dimensions of the first port feedlines 209 are similar to those of the first element 205 and arm connectors 207. For example, the first port feedlines may each have a length K₁ in the direction of elongation of the first and second elements of less than or the same as 1mm.
Figure 4 illustrates an example feeding structure for the first port 202. In this example, the signal 401 being transmitted or received is fed along a central feedline 209b of the set of first port feedlines. This aids in generating a more symmetrical current flow through the radiator, and hence a more uniform radiation pattern.
Figure 5 illustrates a current distribution for a resonance of the antenna structure of figure 2 excited by the first port 202. The resonance shown is at a resonant frequency of 1.8 GHz. This is a symmetrical excited mode in which current flows symmetrically through the radiator 201 from the first port 202. Figure 6 illustrates the radiation pattern for the resonance at the resonant frequency of 1.8 GHz shown in figure 5. The radiation pattern is shown in 3D. The generally uniform shape of the radiation pattern illustrates high isolation between the symmetrical and asymmetrical modes of the antenna structure.
The second port 203 of the antenna structure 200 of figure 2 will now be described. The second port 203 comprises a set of second port feedlines. These second port feedlines are not shown on figure 2. The second port feedlines connect to the second element 206 of the antenna structure. The second port feedlines connect to an opposing side of the second element 206 to the arm connectors 207.
Figures 7 to 10 illustrates example feeding arrangements for the second port. In all of these arrangements, the second port comprises two second port feedlines 701a and 701b. These two feedlines are connected to the second element 206 in a symmetrical arrangement. The two feedlines are connected to a central area of the second element 206. The combination of the second port feedlines 701a, 701b and the second element 206 form a symmetrical structure which has reflectional symmetry about the axis 208. In alternative feeding arrangements, there may be more than two second port feedlines.
In the examples of figures 7 to 10, the second port feedlines extend perpendicularly to the direction of elongation of the second element 206. The second port feedlines are in the same plane as the remainder of the antenna structure. In other words, the second port feedlines and the single radiator 201 form a planar structure. Alternatively, the second port feedlines may extend out of the plane of the single radiator. For example, the second port feedlines may extend perpendicularly to the plane of the single radiator 201. This may aid fitting the antenna structure into the shape of the available volume of the device into which the antenna structure is integrated.
The dimensions of the second port feedlines 701a, 701b are similar to those of the first element 205 and arm connectors 207. For example, the second port feedlines may each have a length K₂ in the direction of elongation of the first and second elements of less than or the same as 1mm.
Figures 7 and 8 illustrate differential feeding structures for the second port. In figure 7, the differential pair of signals 702a, 702b being transmitted or received are fed along second port feedlines 701a, 701b to second element 206. In figure 7, the second element 206 is disconnected in the centre of the antenna structure. A first one of the second port feedlines 701a connects to one end of the disconnected second element 206a in a central region of the first radiator 201. The other end of the first one of the second port feedlines 701a is connected to ground at 703. The second one of the second port feedlines 701b connects to one end of the other disconnected second element 206b in the central region of the first radiator 201. The other end of the second one of the second port feedlines 701b is connected to ground at 704.
In figure 8, the second element 206 is not disconnected in the centre of the antenna structure. The second element 206 is continuous in the central region of the first radiator 201. Each of the second port feedlines 701a, 701b connects to the second element 206 in the central region of the first radiator 201. The signal to be transmitted 801 is fed differentially to the two second port feedlines.
Figure 9 illustrates a coaxial cable feeding structure for the second port. As in figure 7, the second element 206 is disconnected in the centre of the antenna structure. The signal being transmitted or received via the second port is fed through a wire in coaxial cable 901 to a first one of the second port feedlines 701a. This first one of the second port feedlines 701a connects to one end of the disconnected second element 206a in the central region of the first radiator 201. The sheath of the coaxial cable terminates in the ground plane. The second one of the second port feedlines 701b connects the sheath of the coaxial cable to one end of the other disconnected second element 206b in the central region of the first radiator 201 via balun 902.
Figure 10 illustrates a microstrip feeding structure for the second port. The signal being transmitted or received via the second port is fed to or from microstrip 1001. As in figure 7, the second element 206 is disconnected in the centre of the antenna structure. The first one of the second port feedlines 701a connects one end of the disconnected second element 206a in the central region of the first radiator 201 to microstrip 1001. The second one of the second port feedlines 701b connects the end of the other disconnected second element 206b in the central region of the first radiator 201 to microstrip 1001 via balun 1002.
Figure 11 illustrates a current distribution for a resonance of the antenna structure of figure 2 excited by the second port 203. The resonance shown is at a resonant frequency of 2.08 GHz. This is an asymmetrical excited mode in which current flows asymmetrically through the radiator 201 from the second port 203. Figure 12 illustrates the radiation pattern for the resonance at the resonant frequency of 2.08 GHz shown in figure 11. The radiation pattern is shown in 3D. The generally uniform shape of the radiation pattern illustrates high isolation between the symmetrical and asymmetrical modes of the antenna structure.
In addition to the features described above, the feeding structures for the first and second ports may comprise impedance matching network circuitry. This is shown labelled MN on each of the feedlines in figures 4 and 7 to 10. Each impedance matching network circuitry may comprise one or more of the following: inductor(s), capacitor(s), switch(es), and variable capacitor(s). The impedance matching network circuitry transforms the impedance relationship between the circuitry on either side of the matching network circuitry so that their impedances match. This enables the signal power to be efficiently transferred to the antenna from the transmit circuitry during transmission, and power to be efficiently transferred from the antenna to the receive circuitry during reception.
As an example, in the antenna structure of figure 2, the matching network circuitry 2010 may be an inductor, the matching network circuitry 2011 may be a capacitor, the matching network circuitry 2012 may be another inductor, and the matching network circuitry 2014 may be another capacitor.
In the example feeding structure for the first port of the antenna structure shown in figure 4, each of the first port feedlines comprises impedance matching network circuitry 402. For the central first port feedline 209b, the impedance matching network circuitry 402b is located between the signal being applied to the feedline at 401 and the feedline connecting to the first element 205.
In the example feeding structures for the second port of the antenna structure shown in figures 7 and 8, each of the second port feedlines comprises impedance matching network circuitry 705. For both second port feedlines, the impedance matching network circuitry 705a, 705b is located between the signal being applied to the feedline at 702a, 702b and the feedline connecting to the second element 206. In figure 8, further impedance matching network circuitry 802 is integrated into the second element 206 between the points of the second element 206 which connect to the first and second second port feedlines 701a, 701b.
In the example feeding structure for the second port of the antenna structure shown in figure 9, each of the second port feedlines comprises impedance matching network circuitry 903a, 903b. For the first second port feedline 701a, the impedance matching network circuitry 903a is located between the coaxial cable 901 and the connection with the second element 206a. For the second second port feedline 701b, the impedance matching network circuitry 903b is located between the connection with the second element 206b and the balun 902.
In the example feeding structure for the second port of the antenna structure shown in figure 10, each of the second port feedlines comprises impedance matching network circuitry 1003a, 1003b. For the first second port feedline 701a, the impedance matching network circuitry 1003a is located between the microstrip 1001 and the connection with the second element 206a. For the second second port feedline 701b, the impedance matching network circuitry 1003b is located between the connection with the second element 206b and the balun 1002.
As described above, the antenna structure of figure 2 can operate in both a symmetrical excited mode in which a signal is transmitted from or received by the first port 202, and an asymmetrical excited mode in which a signal is transmitted from or received by the second port 203. The two modes are sufficiently well isolated that the antenna structure can simultaneously transceive in the symmetrical mode and the asymmetrical mode. In other words, the antenna structure can: (i) transmit in both the symmetrical and asymmetrical modes at the same time, or (ii) receive in both the symmetrical and asymmetrical modes at the same time, or (iii) transmit in the symmetrical mode and receive in the asymmetrical mode at the same time, or (iv) receive in the symmetrical mode and transmit in the asymmetrical mode at the same time. The resonant frequency of the symmetrical mode may be the same as the resonant frequency of the asymmetrical mode. The resonant frequency of the symmetrical mode may be different to the resonant frequency of the asymmetrical mode.
The antenna structure may additionally be operable to transceive in a further symmetrical mode in which current flows symmetrically through the single radiator 201 to or from the first port 202. This further symmetrical mode causes the single radiator 201 to resonate at a different frequency to the resonant frequency of the first symmetrical mode. Figure 13 illustrates a current distribution for a resonance of the antenna structure of figure 2 excited by the first port 202. The resonance shown is at a resonant frequency of 2.45 GHz. This is a symmetrical excited mode in which current flows symmetrically through the radiator 201 from the first port 202. Figure 14 illustrates the radiation pattern for the resonance at the resonant frequency of 2.45 GHz shown in figure 13. The radiation pattern is shown in 3D. The generally uniform shape of the radiation pattern illustrates high isolation between the symmetrical and asymmetrical modes of the antenna structure.
The antenna structure may additionally be operable to transceive in a further asymmetrical mode in which current flows asymmetrically through the single radiator 201 to or from the second port 203. This further asymmetrical mode causes the single radiator 201 to resonate at a different frequency to the resonant frequency of the first asymmetrical mode. Figure 15 illustrates a current distribution for a resonance of the antenna structure of figure 2 excited by the second port 203. The resonance shown is at a resonant frequency of 2.45 GHz. This is an asymmetrical excited mode in which current flows asymmetrically through the radiator 201 from the second port 203. Figure 16 illustrates the radiation pattern for the resonance at the resonant frequency of 2.45 GHz shown in figure 15. The radiation pattern is shown in 3D. The generally uniform shape of the radiation pattern illustrates high isolation between the symmetrical and asymmetrical modes of the antenna structure.
The antenna structure of figure 2 can transceive in any combination of the first and further symmetrical modes and first and further asymmetrical modes described above at the same time. The term transceive is used herein to mean transmit or receive. Thus, the antenna structure can transmit or receive in any one of the four described modes individually whilst also transmitting or receiving in each of the other three modes. As an example, the antenna structure can receive in all four modes at the same time.
Figures 17 to 19 illustrate the performance of an example embodiment of the antenna structure of figure 2. Figures 17 and 18 show plots of the S parameters S₁₁, S₁₂, S₂₁ and S₂₂ as a function of frequency. S_nm is a transmission coefficient which provides a measure of how much of the signal is transmitted to port n from port m. S_nn is a reflection coefficient which provides a measure of how much of the signal is reflected back to port n from port n. The antenna structure radiates with the greatest power when S₁₁ or S₂₂ are low. Figure 17 shows that the example antenna structure radiates best in the symmetrical mode at 2.45 GHz and 1.8 GHz. These are the two resonant frequencies of that symmetrical mode. Figure 17 shows that the antenna structure radiates best in the asymmetrical mode at 2.45 GHz. This is one resonant frequency of the asymmetrical mode. The other resonant frequency for the asymmetrical mode is at 1.8 GHz, which can be seen more easily on figure 18. Figure 17 shows that the transmission coefficients S₁₂ and S₂₁ are the same. This is because the system is reciprocal. Both these (same) plots are low (below - 20 dB at the resonant frequencies) which demonstrates high isolation between the symmetrical and asymmetrical modes of the antenna structure. Figure 19 illustrates the reflected Envelope Correlation Coefficient (ECC) of the symmetrical and asymmetrical modes of the antenna structure. The ECC is low which demonstrates high isolation between the symmetrical and asymmetrical modes of the antenna structure.
Figures 20 and 21 illustrate the performance of the antenna structure of figure 2 when the second port has the feedline arrangement shown in figure 8, and the first port has the feedline arrangement shown in figure 4. Figure 21 shows extremely high isolation between the symmetrical and asymmetrical modes of the antenna structure, with S₁₂/S₂₁ below -80 dB at the resonant frequencies.
Figure 22 illustrates the current distributions through the antenna structure of figure 2 at the two resonant frequencies of the symmetrical mode and the two resonant frequencies of the asymmetrical mode during signal transmission. In both modes, resonance two is at a higher frequency than resonance one.
For the symmetrical mode, at the lower resonance frequency of resonance one, the current primarily flows through the outer first port feedlines 209a, 209c, through the arm connectors 207, and then in opposing directions along the second element 206. At the higher resonance frequency of resonance two, the current primary flows through the central first port feedline 209b, along the first element 205 in opposing directions, through the arm connectors 207 and then in opposing directions along the second element 206.
For the asymmetrical mode, at the lower resonance frequency of resonance one, the current primarily flows along the second element 206, and then through one arm connector 207, along the first element 205, through the other arm connector 207, then along the second element 206. At the higher resonance frequency of resonance two, the current primarily flows directly along the second element 206.
The single radiator 201 described herein may be fabricated from metal strips or wire. The ground plane 204 may be fabricated from a large piece of metal, such as copper, on a PCB board.
The feedlines described herein may be fabricated over multiple layers. The single radiator 201 described herein may be fabricated over multiple layers. The antenna structure as a whole may be a planar structure. Alternatively, the antenna structure may have a three-dimensional profile. For example, the single radiator 201 may be a planar structure with the feedlines of one or more of the ports extending out from that planar structure. The single radiator 201 may itself have a three-dimensional profile. This may enable the antenna structure to fit into the shape of the available volume in, for example, the mobile phone or tablet into which the antenna structure is incorporated.
The antenna structure described above uses the same single radiator to transceive in both a symmetrical mode and an asymmetrical mode. The single radiator may simultaneously transceive in the symmetrical mode and the asymmetrical mode. In this scenario, current is flowing in different directions on the same single radiator. Thus, it achieves the two resonances of the prior art described herein but in a more compact structure.
The antenna structure described herein is able to resonate at four resonant frequencies in total rather than the two resonances in the prior art described herein. These four resonances are sufficiently well isolated that signals can be transceived on all four resonant frequencies at the same time.
The four resonant frequencies (two in the symmetrical mode and two in the asymmetrical mode) may all be different. Alternatively, a resonant frequency of the symmetrical mode may be the same as a resonant frequency of the asymmetrical mode. By having a resonant frequency of the symmetrical mode match a resonant frequency of the asymmetrical mode, a signal at that resonant frequency will be able to be transmitted or received with a stronger signal strength.
The resonant frequencies of the symmetrical and asymmetrical modes may fall in the range 1.5 to 3 GHz. For example, a resonant frequency may be 1.8 GHz, which is a frequency for transceiving cellular signals. Another resonant frequency may be 2.1 GHz, which is another frequency for transceiving cellular signals. Another resonant frequency may be 2.45 GHz, which is the frequency for transceiving Bluetooth and WiFi signals. The resonant frequencies of the symmetrical and asymmetrical modes may fall in a wider frequency band. For example, resonant frequencies of up to 24 GHz can be supported by the antenna structure. The dimensions of the elements of the antenna structure described above can be adapted to enable them to resonate in different frequency ranges. For example, the antenna elements can be reduced in length to cause them to have higher resonant frequencies. The antenna elements can be increased in length to cause them to have lower resonant frequencies.
This antenna configuration can be used in a range of devices, such as mobile phones, tablets, base stations, radars or antennas mounted on airplanes.
In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention defined only by the appended claims.

Claims

An antenna structure (200) comprising:
a first port (202);

a second port (203); and

a single radiator (201) connected to both the first and second ports (202, 203), the single radiator (201) being operable to simultaneously transceive in:
a symmetrical excited mode in which current flows symmetrically through the single radiator (201) to or from the first port (202), thereby causing the single radiator (201) to resonate at a first resonant frequency; and

an asymmetrical excited mode in which current flows asymmetrically through the single radiator (201) to or from the second port (203), thereby causing the single radiator (201) to resonate at a second resonant frequency,

wherein the single radiator (201) comprises:
a first element (205), the first element (205) being elongate and linear;

a second element (206), the second element (206) being elongate, linear, and parallel to the first element (205); and

arm connectors connecting the first element (205) to the second element (206);

wherein the second port (203) comprises two second port feedlines connected to the second element (206) in a symmetrical arrangement;

wherein the antenna structure (200) is configured to feed a signal being transmitted or received via the second port (203) as a differential signal along the two second port feedlines.
An antenna structure (200) as claimed in claim 1, wherein the single radiator (201) is operable to transceive in a further symmetrical excited mode in which current flows symmetrically through the single radiator (201) to or from the first port (202), thereby causing the single radiator (201) to resonate at a third resonant frequency.
An antenna structure (200) as claimed in claim 2, wherein the single radiator (201) is operable to simultaneously transceive in both the symmetrical excited mode and the further symmetrical excited mode.
An antenna structure (200) as claimed in any preceding claim, wherein the single radiator (201) is operable to transceive in a further asymmetrical excited mode in which current flows asymmetrically through the single radiator (201) to or from the second port (203), thereby causing the single radiator (201) to resonate at a fourth resonant frequency.
An antenna structure (200) as claimed in claim 4, wherein the single radiator (201) is operable to simultaneously transceive in both the asymmetrical excited mode and the further asymmetrical excited mode.
An antenna structure (200) as claimed in claim 1, wherein the first element (205), the second element (206) and arm connectors form a symmetrical structure.
An antenna structure (200) as claimed in claim 1 or 6, wherein the first port (202) comprises a set of first port feedlines connected to the first element (205) in a symmetrical arrangement.
An antenna structure (200) as claimed in claim 7, configured to feed a signal being transmitted or received via the first port (202) along a central first port feedline of the set of first port feedlines.
An antenna structure (200) as claimed in any preceding claim, configured to feed a signal being transmitted or received via the second port (203) through a co-axial cable coupled to a balun or a microstrip coupled to a balun.
An antenna structure (200) as claimed in any preceding claim, wherein each first port feedline and/or each second port feedline comprises impedance matching network circuitry.
An antenna structure (200) as claimed in any preceding claim, having a three-dimensional profile and/or being established partially or wholly of multiple layers.
A method of operating an antenna structure (200) as claimed in any preceding claim, the method comprising:
simultaneously transceiving in:
a symmetrical excited mode in which current flows symmetrically through the single radiator (201) to or from the first port (202), thereby causing the single radiator (201) to resonate at a first resonant frequency; and

an asymmetrical excited mode in which current flows asymmetrically through the single radiator (201) to or from the second port (203), thereby causing the single radiator (201) to resonate at a second resonant frequency,

wherein the single radiator (201) comprises:
a first element (205), the first element (205) being elongate and linear;

a second element (206), the second element (206) being elongate, linear, and parallel to the first element (205); and

arm connectors connecting the first element (205) to the second element (206).